I will spew my train of thought here, maybe redefine some terms hehe. Not that I disagree with what you said.

I never looked at optimism or pessimism as needing specificity in an outcome. It is more as an attitude toward the future and of possibilities, and not knowing. That's what I think of expectation, in that it expresses a specific outcome that I don't think necessarily applies to an attitude.

But then I don't view this as a strict dichotomy but a spectrum of feeling. There's a scale of perceived freedom. In the existential sense of starting with nothing, the optimist sees ways to engage with possibility while the pessimist still sees nothing, within the context of each choice. The pessimist negates what is inherent to them while the optimist perceives various levels of possibility that is subjective to them.

So I see pessimism as seeing no meaningful choice and no freedom, the bottom where we all start, and optimism is any level above that where we actively engage, positivity, as it relates to existentialism. People with more optimism can feel like more is possible, that more choices can be made. Like that Bernard Shaw quote "There are those that look at things the way they are, and ask why? I dream of things that never were, and ask why not?”